E. Lugo-Martinez, N.A. Ulloa-Castillo, M.C. Rodriguez-Aranda
Instituto Tecnologico y de Estudios Superiores de Monterrey,
Mexico
Keywords: BaTiO3, structural transitions, thin films
Summary:
In this study, we investigate the synthesis and structural phase evolution of BaTiO3 thin films produced through thermally activated sintering of composite precursor-based solutions. These composite solutions were created by incorporating a sol-gel precursor with varying concentrations of polyvinylpyrrolidone (PVP). Spin-coated thin films were applied to quartz substrates and sintered at 900 °C. We conducted structural phase characterization using techniques such as X-ray diffraction, Raman spectroscopy, infrared spectroscopy, and thermogravimetric analysis. The thermogravimetric data revealed significant weight loss due to moisture evaporation at around 200 °C, PVP decomposition at approximately 430 °C, and a flash point thermal event at around 450 °C. Structural phase transitions were monitored at temperatures of 400 °C, 500 °C, 700 °C, and 900 °C, showing a progression from an amorphous state to the formation of BaCO3 and the ferroelectric BaTiO3 phase. We observed BaCO3 at 400 °C and 500 °C, while the BaTiO3 phase emerged at 700 °C and 900 °C. Notably, films with higher concentrations of the polymer exhibited an increased content of BaCO3. Additionally, photoluminescence (PL) signals were observed beginning at 400 °C, with emissions evolving throughout the sintering process. Initial emissions were detected at approximately 525 nm, subsequently shifting to 585 nm with increasing sintering temperature. To elucidate the origin of the PL signals, we conducted complementary structural analyses through X-Ray diffraction, Raman spectroscopy, and infrared spectroscopy, which aided in evaluating the band gap energy values linked to the observed luminescence. Morphological investigations of the sintered films revealed the development of relatively homogeneous BaTiO3 thin films characterized by a porous architecture. This porosity became more pronounced in samples containing higher concentrations of PVP, indicating that the polymer significantly influences the film's surface morphology. The findings of this research highlight the potential of using polymer composite precursor solutions as an effective method for synthesizing ferroelectric thin films. By varying the concentrations of PVP, we can achieve enhanced control over the structural phase evolution of BaTiO3, which is essential for tailoring material properties for specific applications in electronic devices and other technological fields. This study offers valuable insights into the synthesis and characterization of ferroelectric materials and establishes a methodology for optimizing thin film properties to improve performance in practical applications.